From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1F749C433E0 for ; Mon, 11 Jan 2021 18:42:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B5CC72251F for ; Mon, 11 Jan 2021 18:42:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390325AbhAKSml (ORCPT ); Mon, 11 Jan 2021 13:42:41 -0500 Received: from mail.kernel.org ([198.145.29.99]:41896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726063AbhAKSml (ORCPT ); Mon, 11 Jan 2021 13:42:41 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 65CE22251F; Mon, 11 Jan 2021 18:41:57 +0000 (UTC) Date: Mon, 11 Jan 2021 18:41:54 +0000 From: Catalin Marinas To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Will Deacon , Mark Rutland , David Brazdil , Alexandru Elisei , Ard Biesheuvel , Jing Zhang , Ajay Patil , Prasad Sodagudi , Srinivas Ramana , James Morse , Julien Thierry , Suzuki K Poulose , kernel-team@android.com Subject: Re: [PATCH v3 09/21] arm64: cpufeature: Add global feature override facility Message-ID: <20210111184154.GC17941@gaia> References: <20210111132811.2455113-1-maz@kernel.org> <20210111132811.2455113-10-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210111132811.2455113-10-maz@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Marc, On Mon, Jan 11, 2021 at 01:27:59PM +0000, Marc Zyngier wrote: > Add a facility to globally override a feature, no matter what > the HW says. Yes, this is dangerous. Yeah, it's dangerous. We can make it less so if we only allow safe values (e.g. lower if FTR_UNSIGNED). > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > index 9a555809b89c..465d2cb63bfc 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -75,6 +75,8 @@ struct arm64_ftr_reg { > u64 sys_val; > u64 user_val; > const struct arm64_ftr_bits *ftr_bits; > + u64 *override_val; > + u64 *override_mask; > }; At the arm64_ftr_reg level, we don't have any information about the safe values for a feature. Could we instead move this to arm64_ftr_bits? We probably only need a single field. When populating the feature values, we can make sure it doesn't go above the hardware one. I attempted a feature modification for MTE here, though I dropped the entire series in the meantime as we clarified the ARM ARM: https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-24-catalin.marinas@arm.com/ Srinivas copied it in his patch (but forgot to give credit ;)): https://lore.kernel.org/linux-arm-msm/1610152163-16554-3-git-send-email-sramana@codeaurora.org/ The above adds a filter function but, instead, just use your mechanism in this series for idreg.feature setting via cmdline. The arm64_ftr_value() function extracts the hardware value and lowers it if a cmdline argument was passed. -- Catalin